I looked up how to check if jQuery is loaded, so here’s a memo.

When you’re just starting to use jQuery, the error ”$ is not defined” often occurs.

The following code uses the typeof operator to check if jQuery is defined, and if it is, it displays an alert.

if(typeof jQuery != "undefined"){ //Check if jQuery is loaded
    $(function(){
        alert('jQuery is ready.')
    });
}

That’s all.

【Reference】

・jQueryが読み込まれているか判別する方法 - 小窓屋めがね (How to Check if jQuery is Loaded - Komadoya Glasses)

・typeof演算子 - 演算子 - JavaScript入門 (typeof Operator - Operators - JavaScript Introduction)

That’s all from the Gemba.